A Numerical Investigation of the Effect of Inlet Preswirl Ratio on Rotordynamic Characteristics of Labyrinth Seal

2017 ◽  
Author(s):  
Tomohiko Tsukuda ◽  
Toshio Hirano ◽  
Cori Watson ◽  
Neal R. Morgan ◽  
Brian K. Weaver ◽  
...  
Keyword(s):  
Flow Model ◽  
Three Dimensional ◽  
Axial Direction ◽  
Labyrinth Seal ◽  
Flow Fields ◽  
Bulk Flow ◽  
The Other ◽  
Circumferential Velocity ◽  
Stiffness Coefficients ◽  
Inlet Swirl

Full three-dimensional CFD simulations are carried out using ANSYS CFX to obtain the detailed flow field and to estimate the rotordynamic coefficients of a labyrinth seal for various inlet swirl ratios. Flow fields in the labyrinth seal with the eccentricity of the rotor are observed in detail and the detailed mechanisms that increase the destabilizing forces at high inlet swirl ratios are discussed based on the fluid governing equations associated with the flow fields. By evaluating the contributions from each term of the governing equation to cross coupled force, it is found that circumferential velocity and circumferential distribution of axial mass flow rate play key roles in generating cross coupled forces. In the case that circumferential velocity is high and decreases along the axial direction, all contributions from each term are positive cross coupled force. On the other hand, in the case that circumferential velocity is low and increases along the axial direction, one contribution is positive but the other is negative. Therefore, cross coupled force can be negative in the local chamber depending on the balance even if circumferential velocity is positive. CFD predictions of cross coupled stiffness coefficients and direct damping coefficients show better agreement with experimental results than a bulk flow model does by considering the force on the rotor in the inlet region. Cross coupled stiffness coefficients derived from the force on the rotor in the seal section agree well with those of the bulk flow model.

A Numerical Investigation of the Effect of Inlet Preswirl Ratio on Rotordynamic Characteristics of Labyrinth Seal

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Tomohiko Tsukuda ◽  
Toshio Hirano ◽  
Cori Watson ◽  
Neal R. Morgan ◽  
Brian K. Weaver ◽  
...  
Keyword(s):  
Flow Model ◽  
Three Dimensional ◽  
Axial Direction ◽  
Labyrinth Seal ◽  
Flow Fields ◽  
Bulk Flow ◽  
The Other ◽  
Circumferential Velocity ◽  
Stiffness Coefficients ◽  
Inlet Swirl

Full three-dimensional (3D) computational fluid dynamics (CFD) simulations are carried out using ANSYS cfx to obtain the detailed flow field and to estimate the rotordynamic coefficients of a labyrinth seal for various inlet swirl ratios. Flow fields in the labyrinth seal with the eccentricity of the rotor are observed in detail and the detailed mechanisms that increase the destabilizing forces at high inlet swirl ratios are discussed based on the fluid governing equations associated with the flow fields. By evaluating the contributions from each term of the governing equation to cross-coupled force, it is found that circumferential velocity and circumferential distribution of axial mass flow rate play key roles in generating cross-coupled forces. In the case that circumferential velocity is high and decreases along the axial direction, all contributions from each term are positive cross-coupled force. On the other hand, in the case that circumferential velocity is low and increases along the axial direction, one contribution is positive but the other is negative. Therefore, cross-coupled force can be negative in the local chamber depending on the balance even if circumferential velocity is positive. CFD predictions of cross-coupled stiffness coefficients and direct damping coefficients show better agreement with experimental results than a bulk flow model does by considering the force on the rotor in the inlet region. Cross-coupled stiffness coefficients derived from the force on the rotor in the seal section agree well with those of the bulk flow model.

Rotordynamic Characterization of Labyrinth Seals in Steam Turbines: Effects of Thermal and Mechanical Loads

2018 ◽  
Author(s):  
Filippo Cangioli ◽  
Steven Chatterton ◽  
Paolo Pennacchi ◽  
Leonardo Nettis ◽  
Lorenzo Ciuchicchi ◽  
...  
Keyword(s):  
Flow Model ◽  
High Pressures ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Critical Conditions ◽  
Accurate Estimation ◽  
Transfer Model ◽  
Steam Turbines ◽  
Labyrinth Seals ◽  
The Stability

Over the last few decades, the increasing demand on efficiency and performance for steam turbines has resulted in OEMs operating machines near critical conditions of their structural and thermal capabilities. Consequently, a more accurate estimation of the dynamic behavior of the machine has become mandatory as well as the stability assessment. Steam turbines are subjected to high temperatures, high pressures and centrifugal forces that could change the nominal geometry, especially the clearance profile in correspondence of the sealing components, occasionally generating a convergent or divergent annulus. In this paper, a new thermo-elasto bulk-flow model for labyrinth seals has been introduced. The model includes the bulk-flow model for estimating the dynamic coefficients, heat transfer model for evaluating the temperature distribution in the rotating and stationary parts and structural-mechanics model for calculating the radial growth. By considering a staggered labyrinth seal installed in the balancing drum of a steam turbine, different inlet pre-swirl ratios, as well as the stability of the seal are investigated in this paper. The model can be extremely useful for the dynamic characterisation of a wide class of labyrinth seals considering the effect of the surrounding environment on the rotordynamic coefficient prediction.

Sensitivity Analysis of the One-Control Volume Bulk-Flow Model for a 14 Teeth-on-Stator Straight-Through Labyrinth Seal

2017 ◽  
Author(s):  
Filippo Cangioli ◽  
Paolo Pennacchi ◽  
Giacomo Riboni ◽  
Giuseppe Vannini ◽  
Lorenzo Ciuchicchi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Friction Factor ◽  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Bulk Flow ◽  
Mathematical Treatment ◽  
Dynamic Coefficients ◽  
The One

Since the 80s, academic research in the rotordynamics field has developed mathematical treatment for the prediction of the dynamic coefficients of sealing components. Dealing with the straight-through labyrinth seal, Iwatsubo [1], at a first stage, and Childs [2], later on, have developed the one-control volume bulk flow model. The model allows evaluating the surrounding fluid forces acting on the rotor, analyzing the fluid dynamics within the seal: the continuity, circumferential momentum and energy equations are solved for each cavity. To consider axial fluid dynamics, correlations, aiming to estimate the leakage and the pressure distribution, are required. Several correlations have been proposed in the literature for the estimation of the leakage, of the kinetic energy carry-over coefficient (KE), of the discharge coefficient and of the friction factor. After decades of research in the field of seal dynamics, the bulk-flow model has been confirmed as the most popular code in the industries, however, it is not clear which is the best set of correlations for the prediction of seal dynamic coefficients. This paper allows identifying the most accurate combination of correlations to be implemented in the bulk-flow model. The correlations are related to: the leakage formula, the flow coefficient, the KE and the friction factor. Investigating the results of several models (32 models), which consider different sets of correlations, in comparison to the experimental data (performed by General Electric Oil & Gas), it is possible to observe the dependence, of the model correlations, on the operating conditions. The experimental results, performed using a 14 teeth-on-stator labyrinth seal, investigate several operating conditions of pressure drop.

Measured Comparison of Leakage and Rotordynamic Characteristics for a Slanted-Tooth and a Straight-Tooth Labyrinth Seal

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Naitik J. Mehta ◽  
Dara W. Childs
Keyword(s):  
Inclination Angle ◽  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Inlet Pressure ◽  
Radial Clearance ◽  
Rotordynamic Coefficients ◽  
Seal Design ◽  
Number Of Teeth

Measured results are presented to compare rotordynamic coefficients and leakage of a slanted-tooth labyrinth seal and a straight-tooth labyrinth seal. Both seals had identical pitch, depth, and number of teeth. The teeth inclination angle of the teeth on the slanted-tooth labyrinth was 65 deg from the normal axis. Experiments were carried out at an inlet pressure of 70 bar-a (1015 psi-a), pressure ratios of 0.4, 0.5, and 0.6, rotor speeds of 10.2, 15.35, and 20.2 krpm, and a radial clearance of 0.2 mm (8 mils). One zero and two positive inlet preswirl ratios were used. The results show only minute difference in the rotordynamic coefficients between the two seals. The slanted-tooth labyrinth seal consistently leaked approximately 10% less at all conditions. Predictions were made using a one control volume bulk-flow model (1CVM) which was developed for a straight-tooth labyrinth seal design. 1CVM under-predicted the rotordynamic coefficients and the leakage.

On the Thermodynamic Process in the Bulk-Flow Model for the Estimation of the Dynamic Coefficients of Labyrinth Seals

2017 ◽  
Author(s):  
Filippo Cangioli ◽  
Paolo Pennacchi ◽  
Giuseppe Vannini ◽  
Lorenzo Ciuchicchi ◽  
Andrea Vania ◽  
...  
Keyword(s):  
Energy Equation ◽  
Flow Model ◽  
State Of The Art ◽  
Control Volume ◽  
Zero Order ◽  
The State ◽  
Bulk Flow ◽  
Thermodynamic Process ◽  
Labyrinth Seals ◽  
Stiffness Coefficients

The influence of sealing components on the stability of turbomachinery has become a key topic because oil and gas market is increasingly requiring high rotational speed and high efficiency, which implies the clearance reduction in the seals. The accurate prediction of the effective damping of the seals is critical to avoid instability issues. In recent years, “negative-swirl” swirl brakes have been employed to reverse the circumferential direction of inlet flow, changing the sign of the cross-coupled stiffness coefficients and generating stabilizing forces. Industries started to investigate, by experiments, the dynamical behavior of labyrinth seals. The experimental results of a 14 teeth-on-stator labyrinth seal with nitrogen, performed in the high-pressure seal test rig owned by GE Oil&Gas, are presented in the paper. Both experimental tests with positive and negative pre-swirl values were performed in order to investigate the pre-swirl effect on the cross-coupled stiffness coefficients. Concerning with the dynamic characterization of the seal, the fluid-structure interaction into the seal can be modelled by the bulk-flow numeric approach that is still more time efficient than computational fluid dynamics (CFD). Dealing with the one-control volume bulk-flow model, the thermodynamic process in the seal is considered isenthalpic, despite an expected enthalpy variation along the seal cavities, both for gas and steam applications. In this paper, the authors improve the state-of-the-art one-control volume bulk-flow model [1], by introducing the effect of the energy equation in the zero-order solution. In this way, the real gas properties are evaluated in a more accurate way because the enthalpy variation, expected through the seal cavities, is taken into account in the model. The authors, considering the energy equation only in the zero-order solution, assume that the enthalpy is not a function of the clearance perturbation (i.e. of the rotor perturbed motion). The energy equation links the continuity and the circumferential momentum equations. The density, in the leakage correlation, depends on the enthalpy, which is calculated (in the energy equation) on the basis of the circumferential velocity and of the fluid/rotor shear stress. Therefore, the leakage mass-flow rate and the fluid thermodynamic properties depend, indirectly, on the shear stresses. This fact is proved in the literature by several CFD simulations that investigate the leakage in the straight-through labyrinth seals, hence, the energy equation allows to better characterize the physics of the problem. Overall, by taking into account the energy equation, a better estimation of the coefficients in the case of negative pre-swirl ratio has been obtained (as it results from the comparison with the experimental benchmark tests). The numerical results are also compared to the state-of-the-art bulk-flow model developed by Thorat and Childs (2010), highlighting the improvement obtained.

On the Thermodynamic Process in the Bulk-Flow Model for the Estimation of the Dynamic Coefficients of Labyrinth Seals

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Filippo Cangioli ◽  
Paolo Pennacchi ◽  
Giuseppe Vannini ◽  
Lorenzo Ciuchicchi ◽  
Andrea Vania ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Energy Equation ◽  
Flow Model ◽  
Experimental Tests ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Labyrinth Seals ◽  
State Problem ◽  
Rotordynamic Coefficients ◽  
Steady State Problem

The impact of sealing equipment on the stability of turbomachineries is a crucial topic because the power generation market is continuously requiring high rotational speed and high performance, leading to the clearance reduction in the seals. The accurate characterization of the rotordynamic coefficients generated by the seals is pivotal to mitigate instability issues. In the paper, the authors propose an improvement of the state-of-the-art one-control volume (1CV) bulk-flow model (Childs and Scharrer, 1986, “An Iwatsubo-Based Solution for Labyrinth Seals: Comparison to Experimental Results,” ASME J. Eng. Gas Turbines Power, 108(2), pp. 325–331) by considering the energy equation in the steady-state problem. Thus, real gas properties can be evaluated in a more accurate way because the enthalpy variation, expected through the seal cavities, is evaluated in the model. The authors assume that the enthalpy is not a function of the clearance perturbation; therefore, the energy equation is considered only in the steady-state problem. The results of experimental tests of a 14 teeth-on-stator (TOS) labyrinth seal, performed in the high-pressure seal test rig owned by GE Oil&Gas, are presented in the paper. Positive and negative preswirl ratios are used in the experimental tests to investigate the effect of the preswirl on the rotordynamic coefficients. Overall, by considering the energy equation, a better numerical estimation of the rotordynamic coefficients for the tests with the negative preswirl ratio has been obtained (as it results from the comparison with the experiments). Finally, the numerical results are compared with a reference bulk-flow model proposed by Thorat and Childs (2010, “Predicted Rotordynamic Behavior of a Labyrinth Seal as Rotor Surface Speed Approaches Mach 1,” ASME J. Eng. Gas Turbines Power, 132(11), p. 112504), highlighting the improvement obtained.

A Bulk Flow Model of a Brush Seal System

1991 ◽  
Author(s):  
R. C. Hendricks ◽  
S. Schlumberger ◽  
M. J. Braun ◽  
F. Choy ◽  
R. L. Mullen
Keyword(s):  
High Speed ◽  
Flow Model ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Model Calculations ◽  
Pressure Drops ◽  
Low Leakage ◽  
Smooth Interface ◽  
Brush Seal ◽  
Contact Seal

Fibers such as fabric and bristles can be readily fabricated into a variety of seal configurations that are compliant and responsive to high speed or lightly loaded systems. A linear, circular, or contoured brush seal system is a contact seal consisting of the bristle pattern and hardened interface. When compared to a labyrinth seal the brush seal system is superior and features low leakage, dynamic stability, and permits compliant structures. But in turn the system usually requires a hardened smooth interface, permits only limited pressure drops. Wear life and wear debris for operations with static or dynamic excitation are largely undetermined. A seal system involves control of fluid within specific boundaries. The brush and rub ring (or rub surface) form a seal system. In this paper, design similitudes, a bulk flow model, and rub ring (interface) coatings are discussed. The bulk flow model calculations are based on flows in porous media and filters. The coatings work is based on our experience and expanded to include current practice.

Three-Dimensional CFD Rotordynamic Analysis of Gas Labyrinth Seals

2001 ◽  
Author(s):  
J. Jeffrey Moore
Keyword(s):  
Shear Stress ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Internal Flow ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Navier Stokes ◽  
Labyrinth Seals ◽  
Navier Stokes Equations ◽  
Rotordynamic Forces

Abstract Labyrinth seals are utilized inside turbomachinery to provide non-contacting control of internal leakage. These seals can also play an important role in determining the rotordynamic stability of the machine. Traditional labyrinth seal models are based on bulk-flow assumptions where the fluid is assumed to behave as a rigid body affected by shear stress at the interfaces. To model the labyrinth seal cavity, a single, driven vortex is assumed and relationships for the shear stress and divergence angle of the through flow jet are developed. These models, while efficient to compute, typically show poor prediction for seals with small clearances, high running speed, and high pressure (Childs, 1993). In an effort to improve the prediction of these components, this work utilizes three-dimensional computational fluid dynamics (CFD) to model the labyrinth seal flow path by solving the Reynolds Averaged Navier Stokes equations. Unlike bulk-flow techniques, CFD makes no fundamental assumptions on geometry, shear stress at the walls, as well as internal flow structure. The method allows modeling of any arbitrarily shaped domain including stepped and interlocking labyrinths with straight or angled teeth. When only leakage prediction is required, an axisymmetric model is created. To calculate rotordynamic forces, a full 3D, eccentric model is solved. The results demonstrate improved leakage and rotordynamic prediction over bulk-flow approaches compared to experimental measurements.

A Method for Evaluating the PIV Measurement Error in a Centrifugal Pump

2007 ◽  
Author(s):  
Hua Yang ◽  
Fang-Ping Tang ◽  
Ji-Ren Zhou ◽  
Chao Liu ◽  
Li-Hong Yu
Keyword(s):  
Centrifugal Pump ◽  
Relative Error ◽  
Three Dimensional ◽  
Mass Conservation ◽  
Axial Direction ◽  
Flow Fields ◽  
Two Dimensional ◽  
Piv Measurement ◽  
Two Dimensional Flow ◽  
Relative Errors

Based on the equation of the mass conservation, a method of relative error analysis is presented in this paper. The two-dimensional and three-dimensional PIV data in the impeller and volute of the centrifugal pump are evaluated by this method. The maximum relative errors of two-dimensional flow fields in the impeller and volute are 2.85% and 10.50% respectively, which of three-dimensional are 3.41% and 2.59% respectively. It indicates that there is acceptable accuracy of the relative error using two-dimensional PIV to measure the flow fields in the impeller. Axial direction velocity can not be neglected near the outlet of the rotating impeller in the volute and the flow fields must be measured by three-dimensional PIV to obtain the reliable experimental data.

Sign in / Sign up

Export Citation Format

Share Document